Device for detecting a combustion chamber pressure of an internal combustion engine

ABSTRACT

A device for detecting a combustion chamber pressure of an internal combustion engine, in particular a gasoline engine. The device includes a sensor housing, the sensor housing being set up to be at least partially introduced into a combustion chamber of the internal combustion engine. At least one mechanical-electrical transducer element is accommodated inside the sensor housing, which is separated from the sensor housing by at least one sensor holder, in particular a sensor holder which at least partially encloses the mechanical-electrical transducer element. The sensor holder has an at least partially rigid design.

RELATED APPLICATION INFORMATION

The present application claims priority to and the benefit of Germanpatent application no. 10 2009 022 539.0, which was filed in Germany onMay 25, 2009, the disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a device for detecting a combustionchamber pressure of an internal combustion engine, which is usable inparticular in gasoline engines.

BACKGROUND INFORMATION

Devices of this type form an essential component of modern enginecontrollers, because the combustion chamber pressure must be detectedvery precisely, in particular for the purpose of reducing emissions.Devices are known from the related art, which have predominantly beendeveloped for diesel engines.

Thus, for example, International patent application WO 2006/089446 A1discusses a component for power or pressure sensors, in particular forinstallation in a glow plug. The component includes a measuring elementin the form of a disc or perforated disc made of piezoelectric materialand electrodes in the form of perforated discs or discs, which pressagainst the measuring element on both sides, having contact points forthe contact to lines. Furthermore, one or more transmission bodiessituated on both sides outside the electrodes are provided. Thedescribed elements are held together by an external, electricallyinsulating film, for example shrink tubing, so that a sensor module isformed. The shrink tubing is used, on the one hand, for electricallyinsulating adjacent components and, on the other hand, for holdingtogether the individual components of the sensor module, in particularduring transport between individual manufacturing stations, until finalassembly is performed.

During manufacturing of combustion chamber pressure sensors which aresuitable for mass production, and which are usable as stand-alonecombustion chamber pressure sensors, in particular for gasoline engines,known design and manufacturing concepts may cause technicaldifficulties, however. Thus, for example, the shrink tubing approachdiscussed in International patent application WO 2006/089446 A1 ispredominantly suitable for cylindrical components. Square or polygonalpiezo-quartzes may not be ideally fixed using this approach, however.Furthermore, in many cases assembly of a sensor module with subsequenttransport is not necessary, because complete final assembly may beperformed in one factory. Transport safety of the sensor module is thusno longer an issue in many cases, but rather recedes duringmanufacturing behind the comparatively complex handling steps in theevent of the shrink tubing.

SUMMARY OF THE INVENTION

Therefore, a device for detecting a combustion chamber pressure of aninternal combustion engine is proposed which meets these challenges. Thedevice is also usable in particular in gasoline engines. The deviceincludes at least one sensor housing, i.e., an element which entirely orpartially encloses further components, such as a sensor housing designedat least partially in the form of a hollow cylinder, for example. Thesensor housing may be made of a metallic material, for example, and isset up to be introduced at least partially into the combustion chamberof the internal combustion engine. For example, the sensor housing maybe fixed directly or indirectly in a combustion chamber wall of theinternal combustion engine, so that the sensor housing protrudes atleast partially, for example, using its front end, into the combustionchamber of the internal combustion engine.

The sensor housing may have an opening, for example a circular orpolygonal opening, which is closed by at least one diaphragm, on thecombustion chamber side. A diaphragm may be understood, for example, asan element which is deformable or movable in at least one direction,which extends perpendicular to an axis of the sensor housing, forexample, whose lateral extension may exceed its thickness by at least afactor of 10, in particular by at least a factor of 100. The diaphragmmay be designed, for example, as a metal diaphragm, such as a metalfilm, and may also be designed in one piece with the sensor housingand/or may be joined non-positively and/or positively and/or integrallyto the sensor housing in the area of the opening. It may particularly bepreferable if the sensor housing has a hollow-cylindrical design atleast in the area of the opening, the diaphragm, for example, beingwelded as a metal diaphragm, for example, on the sensor housing, on theedge of the sensor housing enclosing the opening. Another type ofconnection to the sensor housing is fundamentally possible, however,such as a non-positive connection, for example, by a cap nut. Thediaphragm may close the opening completely pressure-tight, at least inthe range of pressures typically occurring in combustion chambers.

Furthermore, the device includes at least one mechanical-electricaltransducer element in the sensor housing. This is generally to beunderstood as an element which can convert mechanical actions, forexample a force action and/or a pressure action and/or a length changein the transducer element, into electrical signals. Reference isessentially made hereafter to piezoelectric transducer elements.Alternatively or additionally, the mechanical-electrical transducerelement may also, however, include other types of transducer elementswhich are set up to convert mechanical signals into electrical signals.Furthermore, the device may have at least one transmission element,which is implemented separately from the sensor housing, fortransmitting a deformation of the diaphragm to the mechanical-electricaltransducer element. In this way, for example, a deflection of theoptional diaphragm due to the combustion chamber pressure may betransmitted via the transmission element to the mechanical-electricaltransducer element, so that an electrical signal may be generatedcorresponding to the deflection of the diaphragm and thus correspondingto the combustion chamber pressure. A transmission element is to beunderstood fundamentally as an arbitrary element, using which movementsand/or deformations of the diaphragm may also be axially transmitted,which may be essentially rigidly, to the mechanical-electricaltransducer element. For example, the transmission element may have anessentially rod-shaped design and may be supported on an axis of thedevice. A one-piece or multipart design of the transmission element ispossible.

As described above, the transmission element may be situated separatelyfrom the sensor housing. This means that the device may have at leasttwo transmission paths, via which forces and/or length changes incomponents of the device, which are exposed directly to the combustionchamber, for example the diaphragm and/or a front side of the sensorhousing facing toward the combustion chamber, may be transmitted to themechanical-electrical transducer element. Thus, for example, the sensorhousing itself may be a part of a first transmission path, and thetransmission element may be part of a second transmission path, which isessentially not coupled to the first transmission path. For example,thermally caused expansions of the device may be transmitted via thefirst transmission path and the second transmission path to themechanical-electrical transducer element, which may be essentiallywithout coupling of the two paths. This is explained in greater detailhereafter. The first transmission path may concentrically enclose thesecond transmission path.

Because thermally caused expansions of the device are transmittable viaboth transmission paths to the mechanical-electrical transducer element,it may particularly be preferable if the device has at least onecompensation body for compensating for different thermal expansions inthe two transmission paths. It may particularly be preferable if thetransmission element itself includes at least one compensation body,which is set up to compensate for differing thermal expansions betweenthe first transmission path and the second transmission path. Thus, forexample, the compensation body may be set up with respect to its lengthand its thermal expansion coefficients in such a way that it ensures, atleast within typical temperature ranges to which the device may beexposed (for example −40° C. to 555° C.), that the thermal expansions ofthe first and the second transmission paths are at least largelyidentical, for example, within the scope of a tolerable deviation of notgreater than 20%, in particular not greater than 10%, and particularlymay be not greater than 5% or even 0%.

For example, in the event of a cold start, temperatures of −40° C. maybriefly prevail. During operation, the described transmission pathtypically does not heat through homogeneously, but rather a temperaturegradient will normally result from the combustion chamber, for example,at a diaphragm temperature of up to approximately 550° C., or to themechanical-electrical transducer element, for example, at a temperatureof the piezo-quartz of up to approximately 200° C. The temperaturecompensation may then be performed, for example, on the basis ofempirically ascertained temperature gradients, for example, ascertainedfrom engine measurements. A temperature compensation may typically onlybe designed either for homogeneous temperatures or for temperaturegradients, in particular homogeneous temperature gradients. Thetemperature compensation may be performed in such a way that apretensioning force, for example, a pretensioning force of themechanical-electrical transducer element, does not change or onlychanges insignificantly upon the transition from an idle temperaturegradient to a full load temperature gradient or vice versa. A change inthe pretensioning force by changing the ambient temperature may normallybe tolerated in this case, because typically a high time constant isprovided and the influence of the measuring signal is usuallynegligible, in particular in connection with a reset of a measuringsignal, for example, after each cycle. It may thus be ensured, forexample, that over the typically occurring temperature range in whichthe device is used, a solely thermally caused transducer signal or achange in the transducer signal of the mechanical-electrical transducerdue to differing expansions in the first transmission path and in thesecond transmission path occurs as little possible. As described above,however, this may also be alternatively or additionally achieved bysituating the at least one compensation body at another location in oneof the two transmission paths and/or by suitable material selection ofthe elements which participate in the transmission paths.

Alternatively or additionally to the at least one compensation body, thetransmission element may also have at least one heat protectioninsulating body having thermally insulating properties. In this way, itmay be ensured that high temperatures and/or large quantities of heatmay not be transmitted via the transmission element from the combustionchamber to the mechanical-electrical transducer element, which coulddamage it. For example, the heat protection insulating body may includeat least one ceramic material, which may have high thermally insulatingproperties. Other types of materials are also possible. The heatprotection insulating body may thus also be constructed in multipleparts. Alternatively or additionally to thermal insulation, the heatprotection insulating body may also have electrically insulatingproperties. This may be ensured in that the thermal protectioninsulating body having the thermally insulating properties also haselectrically insulating properties itself. Alternatively, however, amultipart construction may also be provided, in which the heatprotection insulating body has at least one electrically insulatingcomponent in addition to at least one thermally insulating component.

Furthermore, the device may include at least one contact element forelectrical contacting of the mechanical-electrical transducer element.In particular, this may be a rigid contact element, i.e., a contactelement which only changes its shape insignificantly or not at all underthe effect of its intrinsic weight force. In particular, the contactelement may include at least one busbar, i.e., a rigid element which hascurrent-conducting properties, for example a metallic element. Thecontact element may be set up in such a way that it has at least partialaxial flexibility, for example, sectionally, i.e., a flexibility in itslongitudinal extension direction, for example, parallel to the axis ofthe device. This may be achieved, for example, in that the contactelement is at least partially designed to have elastic properties.Alternatively or additionally, the contact element, for example the atleast one busbar, may at least sectionally allow flexibility in thesensor longitudinal direction in that a double strand is provided. Thismay be performed similarly to corrugated cardboard, for example, in thata busbar is equipped with two external tracks, between which at leastone elastic element is provided, for example a folded metal track. Inthis way, in particular in the area of a contact of themechanical-electrical transducer element, axial flexibility of thecontact element may be provided, for example, in that the contactelement is designed in such a way, for example, bent, that it has one ormore sections having an extension perpendicular to the axis. In this wayor in another way, the one or more contact element(s) may contribute toa strain relief of the mechanical-electrical transducer element, sothat, for example, a force action is possible on themechanical-electrical transducer element, but a travel which isimpressed by tensionings on the mechanical-electrical transducer elementis reduced, for example. However, this travel is significant for anerror signal generated by the tensionings in the mechanical-electricaltransducer element, for example a piezo-quartz.

The mechanical-electrical transducer element may be directly orindirectly supported against an insulating body on its side facing awayfrom the combustion chamber. This insulating body may have electricallyinsulating properties, for example. Furthermore, themechanical-electrical transducer element may alternatively oradditionally be supported directly or indirectly against the sensorhousing via at least one fixing unit on its side facing away from thecombustion chamber. The fixing unit may be a metal fixing unit, forexample, such as a metal ring, which may be integrally and/or positivelyand/or non-positively joined to the sensor housing, for example. Weldingof the fixing unit to the sensor housing may particularly be done. Otherfixing units may also be used, however.

Furthermore, the device has at least one sensor holder. Themechanical-electrical transducer element is separated from the sensorhousing by the at least one sensor holder. The sensor holder has an atleast partially rigid design, i.e., from a material which deforms onlyinsignificantly or not at all at least under the effect of its intrinsicweight force. The sensor holder is thus designed in particular as adimensionally stable component, for example, as a dimensionally stableplastic component, in particular as a thermoplastic component. Inparticular, the sensor holder may have an incompressible design. Thesensor holder may particularly have electrically insulating properties.

In particular, the sensor holder may be at least partially made of oneor more of the following materials: a plastic, in particular a filledplastic, in particular a plastic having a glass-fiber reinforcement; apolyetherimide (PEI); a polyetheretherketone (PEEK); a ceramic; apolymer ceramic. The use of other materials is also fundamentallypossible, however. The plastic, in particular the filled plastic, mayinclude, for example, as noted, a polyetherimide and/or apolyetheretherketone, and/or also a polyamide and/or a polypropyleneand/or a polyphenylene sulfide (PPS). Alternatively or additionally to aglass-fiber filling, other fillers may also be used, for example carbonfibers and/or ceramics or similar materials.

In particular, the sensor holder may also be designed as a sensor holderwhich at least partially encompasses, in particular encloses, themechanical-electrical transducer element, for example, a sensor holderwhich concentrically encloses this transducer element. Themechanical-electrical transducer element may in particular have apolygonal cross section, in particular a square cross section, thesensor housing being able to have an inner chamber having a round crosssection, in particular a circular cross section. In this way, the sensorholder may be used as a geometrical adapter, for example, in order tohold a polygonal mechanical-electrical transducer element securely,reliably, and with little play inside the sensor housing. The sensorholder may be at least partially designed as a sleeve, for example. Thesensor holder may have an external diameter of less than 8 mm and whichmay be less than 4.5 mm, for example. The sensor holder, as noted above,may have thermally and/or electrically insulating properties, forexample, and/or vibration-damping properties.

The sensor holder may also at least partially enclose at least a part ofthe transmission element, for example the heat protection insulatingbody and/or the compensation body. Alternatively or additionally, thesensor holder may also entirely or partially enclose the insulatingbody. In this way, the two above-described transmission paths may beadditionally separated from one another. The sensor holder itself shouldnot have any direct contact with the diaphragm, so that the sensorholder itself does not form a component of the above-mentionedtransmission paths. Alternatively or additionally, the sensor holder mayenclose further elements of the device, in particular further elementswhich form part of the second transmission path. The sensor holder maythus at least partially enclose elements, for example the insulatingbody, on the side of the mechanical-electrical transducer element facingaway from the combustion chamber.

Furthermore, the sensor holder may have at least one, and may have two,three, four, or more axial guide elements in its inner and/or on itsouter surface pointing toward the sensor housing. Axial guide elementsare generally to be understood as spacers which extend in the axialdirection. In particular, these may be elements which are set up inorder to hold and/or guide the element or elements enclosed by thesensor holder at a distance from an inner wall of the sensor holder andreduce friction losses in this way. Alternatively or additionally, theaxial guide elements may also include one or more elements which are setup in order to hold and/or guide the external surface of the sensorholder facing toward the sensor housing at a distance from the innerwall of the sensor housing and to reduce friction losses in this way.For example, the sensor holder may have, as the at least one axial guideelement, at least one axially running rib for friction reduction. Thegoal of these measures may be minimization of friction to the firsttransmission path and/or to the second transmission path, i.e., forexample, minimization of friction to an external force path and/orminimization of a friction to an internal force path. This at least onerib may extend over the entire length of the sensor holder or over onlya part of the sensor holder, for example.

In this way, in particular components of the second transmission pathdescribed above may be guided inside the sensor holder with reducedfriction. In particular, as described above, the transmission element(in particular the compensation body and/or the heat protectioninsulating body) and/or the first busbar and/or the mechanical andelectrical transducer element (in particular the piezo-quartz) and/orthe second busbar and/or the insulating body may be entirely orpartially guided inside the sensor holder using the at least one axialguide element. The sensor holder may, notwithstanding an optionalexternal cylindrical surface, be adapted by its geometrical design inparticular in such a way that it may optimally receive the elementswhich the sensor holder encloses entirely or partially. Thus, inparticular, an inner chamber of the sensor holder may be geometricallyadapted to the external dimensions of the enclosed elements, optionallywith required play added. If the device, as described above, includes atleast one contact element for electrical contacting of themechanical-electrical transducer element, in particular at least onebusbar, the sensor element may also entirely or partially enclose thiscontact element. In this case, the sensor holder may have at least onerecess, for example an axially running recess, for receiving and/orguiding the contact element. This recess may, for example, be at leastone slot, for example a lateral slot. The device may further include atleast one sealing housing which at least partially encloses the sensorhousing, for example a sealing cone housing. This sealing housing may beset up to allow fixing of the device in a combustion chamber wall, sothat at least a pressure on the combustion chamber side may be appliedto the diaphragm.

The proposed device has numerous advantages with respect to knowndevices in one or more of the above-described specific embodiments,which are positively noticeable in particular when used in gasolineengines. The device is thus designed in such a way that the hightemperatures occurring during combustion in the combustion chamber mayinfluence the signals only insignificantly or not at all. The pressuresignal from the combustion chamber may be relayed within the device intoan area in which temperatures compatible with the mechanical-electricaltransducer element prevail. The proposed construction additionallyallows a measuring signal transmission with minimal signal reductionand/or signal change. Furthermore, external mechanical influences, forexample the screwing-in torque, are kept away from the secondtransmission path, i.e., from the transmission path of the pressure, theforce, and the electrical signal.

Through the proposed second transmission path, which may be used as arelevant force path and whose transmission is received by themechanical-electrical transducer element, the pressure signal may beconverted with low losses into a force, relayed to the measuringelement, and converted into an electrical signal therein, which is inturn guided to an analysis circuit—integrated in the device itselfand/or situated entirely or partially outside the device. Themechanical-electrical transducer element and/or the analysis element maybe situated in areas having compatible temperatures. Furthermore, theabove-described components of the device may be optimized in such a waythat the measuring signal is not impaired by mechanical and/or thermalinfluences. Thus, in particular temperature influences and/or mechanicalinfluences which may occur due to the busbars, for example, may beminimized by the above-described embodiment according to the presentinvention.

Using the proposed device, in particular an efficient alternative to theknown shrink tubing approaches for holding the sensor module may beprovided. Using a specially profiled sensor holder, for example aspecially profiled plastic body, instead of the shrink tubing, inparticular the assembly of the sensor module, which may also encloseparts of the transmission element and/or the insulating body in additionto the mechanical-electrical transducer element, may be made easier. Inaddition, a square or polygonal piezo-quartz may be manufactured morecost-effectively than a cylindrical one, the assembly of squarepiezo-quartzes in a round sensor housing being made possible using theprefinished sensor holder. Furthermore, pre-assembly of a sensor moduleat a supplier is not necessary, and the entire assembly may be performedin one final assembly factory.

In this way, transport safety of the sensor module may be dispensed withas a requirement, because it may now be necessary to provide a singlecomponent, which holds the adjacent components in the intended locationduring operation, and no longer during the transport of the sensormodule. The design of the sensor holder is comparatively free. Inparticular, a design as a plastic component, for example, as aninjection-molded plastic component, is relatively free in its design, sothat the sensor holder allows, for example, the transition from a squarepiezo-quartz and/or another mechanical-electrical transducer element toa round sensor housing in the radial direction, for example. On theother hand, a transition from a square and/or polygonalmechanical-electrical transducer element to a differently designed bodymay also be made possible in the axial direction, for example, tosurrounding insulating bodies and/or transmission elements, which mayhave a round design, for example.

Using the at least one axial guide element, for example the rib,low-friction guiding of the second transmission path in the sensorholder and thus minimization of hysteresis may be ensured. In this way,minimization of hysteresis errors may in turn be achieved. Furthermore,effective electrical insulation of the mechanical-electrical transducerelement, for example the piezo-quartz, and optionally the componentswhich conduct the sensor signal (for example the busbars) from theexternal housing may be ensured.

Exemplary embodiments of the present invention are shown in the drawingsand are described in greater detail in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a device according to thepresent invention for detecting a combustion chamber pressure of aninternal combustion engine.

FIG. 2A shows a perspective illustration of an exemplary embodiment of asensor holder.

FIG. 2B shows another perspective illustration of an exemplaryembodiment of a sensor holder.

FIG. 2C shows another perspective illustration of an exemplaryembodiment of a sensor holder.

FIG. 2D shows another perspective illustration of an exemplaryembodiment of a sensor holder.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of a device 110 according to thepresent invention for detecting a combustion chamber pressure of aninternal combustion engine, which may be used in particular in agasoline engine. Device 110 includes a housing 112 constructed inmultiple parts, having a main body 114 and a sealing housing 118,designed as a sealing cone housing 116, having a sealing cone 120 on thecombustion chamber side. Main body 114, which may be made of a plasticmaterial and/or a ceramic material, for example, receives a contactmodule 122. Signals of device 110 may already be entirely or partiallyprocessed in this contact module 122 and/or relayed outward via one ormore interfaces (not shown in FIG. 1). Sealing housing 118, which has anessentially cylindrical design, and which in turn concentricallyencloses a sensor housing 124, is placed on the main body. This sensorhousing 124 has an opening 128, which is closed by a diaphragm 130, onits side facing toward a combustion chamber 126. This diaphragm 130 isset up to deform or bend in a direction of an axis 132 of device 110upon actions of a pressure from combustion chamber 126.

A compensation body 134 is attached to diaphragm 130 in the interior ofsensor housing 124 along axis 132. This is in turn adjoined in the axialdirection by a heat protection insulating body 136, which opens on afirst contact area extending essentially perpendicular to axis 132 of afirst busbar 140, which otherwise extends essentially parallel to axis132. A mechanical-electrical transducer element 142 in the form of apiezo-quartz 144 adjoins this busbar. The side of piezo-quartz 144facing away from combustion chamber 126 is adjoined in the axialdirection by a second contact area 146, which is implemented as asection extending essentially perpendicular to axis 132 of a secondbusbar 148, which otherwise may extend essentially parallel to axis 132.Both contact areas 138 and 146 form contacts and/or electrodes ofpiezo-quartz 144. Alternatively, electrodes of piezo-quartz 144 may alsobe designed in another way and/or as components separate from busbars140, 148.

An insulating body 150 adjoins second contact area 146 in the axialdirection on the side of piezo-quartz 144 facing away from combustionchamber 126. Insulating body 150 has a section 152 on the combustionchamber side having a reduced diameter, which is enclosed, together withpiezo-quartz 144 and heat protection insulating body 136, by a sensorholder 154. A fixing unit 156 in the form of a metal ring adjoins theinsulating body in the axial direction on the side facing away fromcombustion chamber 126. This metal ring may be welded to sensor housing124, for example, as described in greater detail below. The metal ringof fixing unit 156 in turn encloses an insulating sleeve 158 in theexemplary embodiment shown, via which fixing unit 156 is separated froman extension 160 of insulating body 150.

Device 110, which is designed as a combustion chamber pressure sensor,protrudes on the diaphragm side into combustion chamber 126 of theinternal combustion engine. The pressure applied in the combustionchamber is converted into a force inside diaphragm 130, which acts oncompensation body 134. Compensation body 134 has the function, on theone hand, of relaying the force to heat protection insulating body 136,which forms a transmission element 162 together with compensation body134. On the other hand, compensation body 134 has the function ofcompensating for differing thermal expansions of adjacent components.Piezo-quartz 144 is part of a structure which has two paralleltransmission paths. A first transmission path may include diaphragm 130,sensor housing 124, and fixing unit 156. A second transmission path mayinclude diaphragm 130, compensation body 134, heat protection insulatingbody 136, first busbar 140 or its first contact area 136, piezo-quartz144, second busbar 148 or its second contact area 146, insulating body150, and fixing unit 156.

The inner, second transmission path expands differently than the outer,second transmission path enclosing it because of differing thermalexpansion coefficients of these components. These differing expansionsfinally result in additional loading or relief of piezo-quartz 144,which is superimposed with the force action resulting from thecombustion chamber pressure and typically may not be differentiatedtherefrom.

This superposition thus typically results in a measuring error. It istherefore proposed according to the exemplary embodiments and/or theexemplary methods of the present invention that the differing expansionsbe suppressed in that compensation body 134 may be configured withrespect to its length and/or its coefficient of thermal expansion insuch a way that it ensures that the thermal expansions of the inner andthe outer transmission paths are identical. However, this expansion isonly possible for a specific temperature or a specific temperaturegradient in many cases. Nonetheless, using a suitable material selectionof compensation body 134, at least a minimization of expansion errors asa result of differing thermal expansions in the transmission paths maybe achieved at least in the relevant temperature range of device 110.

Heat protection insulating body 136 has the function, on the one hand,of interrupting the thermal path from combustion chamber 126 topiezo-quartz 144, i.e., protecting piezo-quartz 144 from overheating. Onthe other hand, it may also be used as an electrical insulator, whichensures that the electrical charges transmitted from piezo-quartz 144 tobusbars 140, 148 are only relayed on the route provided for them viabusbars 140, 148 themselves. Depending on the concrete requirements forthe electrical insulation and/or the thermal insulation, it may beadvisable or necessary to design heat protection insulating body 136 inmultiple parts, and to divide it into a thermally insulating componentand an electrically insulating component, for example, whose materialsmay then be optimized for the corresponding requirements.

Piezo-quartz 144 is made of piezoelectric material and converts a force,the force resulting from the combustion chamber pressure signal here,into an electrical charge, which is proportional to the applied force,i.e., to the applied pressure here. Piezo-quartz 144 converts the forcevia the detour of a length change into an electrical charge. Theelectrical charge is converted into a voltage proportional to the chargeand/or the force and/or the pressure, which may then be relayed to anengine control unit, in an analysis circuit (not shown in FIG. 1), forexample, which may be entirely or partially accommodated in contactmodule 122, but which may alternatively or additionally also be entirelyor partially accommodated outside device 110.

Busbars 140, 148 each have essentially the same functions. On the onehand, they transmit the charges which are generated in piezo-quartz 144to the analysis circuit. Because a force action, which may in turngenerate an error-relevant measuring signal, may also arise onpiezo-quartz 144 by tensionings in busbars 140, 148 themselves, whichmay arise through thermal expansions or through internal mechanicalstresses after the welding of the busbars to the other components in therear part of device 110 facing away from combustion chamber 126, thebusbars may have a tension relief function. The busbars may accordinglyhave a double strand, in particular in the area between insulating body150 and fixing unit 156, which allows a certain flexibility in thesensor longitudinal direction, i.e., along axis 132. For this purpose,busbars 140, 148 may be designed like corrugated cardboard, as describedabove. Alternatively or additionally, as indicated in FIG. 1, busbars140, 148 may also have one or more folds and/or bends, which are used asspring elements and may ensure the described tension relief. Busbars140, 148 may also be elastic in another way, i.e., have an elasticaction in the direction of axis 132. The force action of tensionings onpiezo-quartz 144 is not reduced by the described flexibility, but theimpressed travel is reduced. The impressed travel, i.e., the change inpiezo-quartz 144, is decisive for the generated error signal inpiezo-quartz 144.

Insulating body 150, which may be made of a ceramic material and/or aplastic material, for example, has the main function of electricallyinsulating piezo-quartz 144 and one or both of busbars 140, 148, forexample second bulbar 148, from adjacent components. Furthermore,insulating body 150 offers space for busbars 140, 148, so that they maybe guided to the analysis circuit. In particular, insulating body 150may also offer space for tension relief strands 164 and/or other typesof spring elements of busbars 140, 148, in order to achieve the tensionrelief action described above. Fixing unit 156, which is configured as ametal fixing unit, for example, is used as a buttress for the previouslydescribed second transmission path, i.e., the inner force path. It maybe welded to sensor housing 124 in the first transmission path, i.e.,the outer force path. The welding may be performed under application ofa pre-stress, for example, which may be necessary so that all componentsrest securely and solidly on one another in every operating state. Inaddition, a pre-stress of this type may be necessary for the mode ofoperation of piezo-quartz 144. Insulating sleeve 158 is used for thepurpose of avoiding an electrical short-circuit between busbars 140, 148and fixing unit 156, also under high mechanical loads during use ofdevice 110, e.g., mechanical shocks.

The first transmission path, i.e., the outer force path, also beginswith above-described diaphragm 130, which may be welded onto sensorhousing 124 in the area of opening 128, for example. Sensor housing 124is used as a carrier of the components of the second transmission path,i.e., the inner force path, and for the purpose of protecting them fromexternal mechanical influences. The rear end of sensor housing 124 maybe welded to fixing unit 156, as described above. Sensor holder 154 issituated between sensor housing 124 and the inner force path. Thissensor holder may be entirely or partially made of plastic, ceramic,polyceramic, or similar material, for example, as a one-piece,sleeve-shaped part, for example. Furthermore, it may be set up for thepurpose of orienting, receiving, and electrically insulatingpiezo-quartz 144, busbars 140, 148, heat protection insulating body 136,and insulating body 150 in relation to sensor housing 124. Sensorhousing 124 encloses the inner force path and forms an independentassembly which contains the entire sensor function and may theoreticallyfunction as a separate sensor, because diaphragm 130 and fixing unit 156are welded to sensor housing 124, in cooperation with the inner and theouter force paths. This sensor functional assembly is still accommodatedin sealing housing 118 in this exemplary embodiment, for example, weldedinto sealing cone housing 116. A structure may thus be achieved whichmay be screwed by a user into a cylinder head. High torques (screwingtorques) and high axial pre-stresses arise as it is screwed in. Theseaxial pre-stresses could induce measuring errors if they acted on thesensor functional assembly. The sensor functional assembly is thereforeonly peripherally welded into sealing cone housing 116 at one point. Atransmission of axial pre-stress forces or torques to the sensorfunctional assembly may therefore be largely prevented. The tightness ofthe sensor inner chamber is simultaneously also implemented by thewelding of the sensor functional assembly to sealing cone housing 116.

An example of a sensor holder 154, which may be used in device 110according to FIG. 1, for example, is shown in various perspective viewsin FIGS. 2A through 2D. Sensor holder 154 has an essentially cylindricalshape on the outside, including an essentially circular-cylindricalsurface 166. Sensor holder 154 may be made of a plastic; however,ceramics and/or polymer ceramics may also be used alternatively oradditionally, as described above. A component made of plastic may bedesigned relatively freely. This circumstance may be exploited in orderto form a component which may allow the transition between a squarepiezo-quartz 144 to a cylindrical sensor housing 124 using its geometryin the radial direction. Sensor housing 124 may have a cylindricaldesign, because this shape is the most cost-effective to manufacture.Piezo-quartz 144 is in turn most cost-effective if it has a squareand/or polygonal design. A plastic component may always be manufacturedcost-effectively, independently of its concrete geometry. Sensor holder154 made of plastic is thus an ideal component, which makes it possiblefor it and adjacent components to be manufactured cost-effectivelywithout functional restriction.

For the same above-described reasons, sensor holder 154 also allows thetransition from piezo-quartz 144 to the elements situated in front ofand/or behind it in the axial direction, such as heat protectioninsulating body 136 and/or insulating body 150, for example, which maybe made entirely or partially of ceramic and which may also be entirelyor partially enclosed by sensor holder 154. These elements may becomponents which may perform the actual transition from polygonal toround themselves, because ceramic components, similarly to plastics, maytypically be designed relatively freely, although with restrictions incomparison to plastic. However, these components may be guided entirelyor partially by sensor holder 154 itself, so that this sensor holder 154may also support the transition from polygonal to round in the axialdirection. In order to avoid or at least reduce hysteresis errors in thesensor, in the ideal case, the components of the second transmissionpath, i.e., the sensor force path, i.e., for example, diaphragm 130,compensation body 134, heat protection insulating body 136, first busbar140, piezo-quartz 144, second busbar 148, insulating body 150, andfixing unit 156, should not contact the adjacent components in theradial direction or should contact them with the smallest possiblecontact surface. Contact causes friction, and a friction of this typemay cause hysteresis.

The hysteresis in turn causes measuring errors. Because sensor holder154 may also have the function of guiding the force travel components,and this may only be implemented with a certain amount of contact, theextent of the contact is to be minimized. For this purpose, in theexemplary embodiment in FIGS. 2A through 2D, axial guide elements 168 inthe form of ribs 170 are provided. In the exemplary embodiment shown,eight ribs 170 of this type are provided, which extend in the interiorof an opening 172 in the radial direction. These small ribs 170 mayensure that for the case in which contact is unavoidable, it is onlyminimal and is not over a large area. Ribs 170 should be provided on theinner side of sensor holder 154, i.e., the side facing towardpiezo-quartz 144. Depending on the assembly concept, these axial guideelements 168 may also, however, alternatively or additionally besituated on outer surface 166 pointing toward sensor housing 124.

A further function of sensor holder 154 may include the electricalinsulation of piezo-quartz 144 and busbars 140, 148 in relation tosensor housing 124. Sensor holder 154 may fulfill this function wellinnately in particular as a plastic component. Experience has shown,however, that particularly high demands are placed on the electricalinsulation capability for a pressure measuring concept which is based ona piezo-quartz 144. Therefore, for example, a polyetherimide, optionallyhaving a glass-fiber reinforcement, may be proposed, because thismaterial is distinguished by a particularly high electrical insulationcapability, which drops only slightly even at high humidity and hightemperatures. Alternatively, for example, PEEK is also conceivable, butis less favorable from cost aspects.

In the exemplary embodiment shown in FIGS. 2A through 2D, sensor holder154 may further include one or more recesses 174 in the presentexemplary embodiment, which are designed here as lateral slots 176 forreceiving busbars 140, 148. Through these two slots 176, it is possibleto lead busbars 140, 148 away from piezo-quartz 144, without additionalradial installation space being required. The wall thickness of sensorholder 154 may be adapted to the geometry of busbars 140, 148 (andoptionally vice versa), in such a way that, on the one hand, asdescribed above, no additional radial space is required, but, on theother hand, busbars 140, 148 may also be prevented from protrudingbeyond the external contour of sensor holder 154, also in considerationof the tolerances. In this way, a short-circuit between busbars 140, 148and sensor housing 124 may be prevented. Sensor holder 154 may have anexternal diameter of less than 4.5 mm.

1. A device for detecting a combustion chamber pressure of an internalcombustion engine, comprising: at least one mechanical-electricaltransducer element; at least one sensor holder; and a sensor housing,wherein the sensor housing is set up to be introduced at least partiallyinto a combustion chamber of the internal combustion engine, wherein theat least one mechanical-electrical transducer element is accommodatedinside the sensor holder, the sensor holder being accommodated insidethe sensor housing, and the sensor holder is axially movable relative tothe sensor housing, wherein the mechanical-electrical transducer elementis separated from the sensor housing by the at least one sensor holder,and wherein the sensor holder has an at least partially rigidconfiguration.
 2. The device of claim 1, wherein the sensor holder haselectrically insulating properties.
 3. The device of claim 1, whereinthe sensor holder is at least partially made of at least one of thefollowing materials: a plastic; a polyetherimide; apolyetheretherketone; a polyphenylene sulfide; a ceramic; and a polymerceramic.
 4. The device of claim 1, wherein the sensor holder has anexternal diameter of less than 8 mm.
 5. The device of claim 1, whereinthe mechanical-electrical transducer element has a polygonalcross-section, and the sensor housing has an inner chamber having around cross section.
 6. The device of claim 1, further comprising: atleast one transmission element, which is implemented separately from thesensor housing, for transmitting a deformation of at least one diaphragmto the mechanical-electrical transducer element, wherein the sensorhousing has an opening on the combustion chamber side which is closed bythe at least one diaphragm, and wherein the sensor holder at leastpartially encloses the transmission element.
 7. The device of claim 6,wherein the sensor housing is part of a first transmission path, whereinthe transmission element is part of a second transmission path, whereinthermally caused expansions of the device are transmittable to themechanical-electrical transducer element via the first transmission pathand the second transmission path, wherein the transmission elementincludes at least one compensation body, and wherein the compensationbody is set up to at least largely compensate for differing thermalexpansions between the first transmission path and the secondtransmission path.
 8. The device of claim 1, wherein the sensor holderhas at least one axial guide element in its interior for frictionreduction.
 9. The device of claim 1, wherein the sensor holder has atleast one axial guide element for friction reduction on its surfacepointing toward the sensor housing.
 10. The device of claim 1, furthercomprising: at least one contact element for electrically contacting themechanical-electrical transducer element, wherein the sensor holder hasat least one recess for at least one of receiving and guiding thecontact element.
 11. The device of claim 1, wherein themechanical-electrical transducer element is supported one of directlyand indirectly against an insulating body on its side facing away fromthe combustion chamber, wherein the insulating body has at leastelectrically insulating properties, and wherein the insulating body isat least partially enclosed by the sensor holder.
 12. The device ofclaim 1, wherein the sensor holder at least partially encloses themechanical-electrical transducer element.
 13. The device of claim 3,wherein the plastic includes one of a filled plastic, and a plastichaving a glass-fiber reinforcement.
 14. The device of claim 1, whereinthe sensor holder has an external diameter of less than 4.5 mm.
 15. Thedevice of claim 1, wherein the mechanical-electrical transducer elementhas a polygonal cross-section, which is a square cross-section, and thesensor housing has an inner chamber having a round cross-section, whichis a circular cross-section.
 16. The device of claim 1, wherein thesensor holder has at least one axial guide element in its interior,which includes at least one axially running rib, for friction reduction.17. The device of claim 1, wherein the sensor holder has at least oneaxial guide element, which includes at least one axially running rib,for friction reduction on its surface pointing toward the sensorhousing.
 18. The device of claim 1, further comprising: at least onecontact element for electrically contacting the mechanical-electricaltransducer element, which includes at least one busbar, wherein thesensor holder has at least one recess for at least one of receiving andguiding the contact element, which includes at least one lateral slot.